The technology for touch control panels generally can be categorized into several types, such as Film on Glass, capacitance, supersonic, optical (infrared light) and the like. In the global market of the touch control panels, Film on Glass has the greatest market share, about 60%. The capacitance type has about 24%, and is mostly for the high unit price market at the dimension of 10.4 inches or more, and is mainly used on information guide systems in public locations such as libraries, railway and bus stations, ATMs in banking, and the like. It has advantages such as water-proof, scrape resistant, higher light permeability and applicable in a wide range of temperature. However, it also has drawbacks such as requiring more manufacturing processes and complex driving IC and circuits. Hence it is not desirable for products of medium and small sizes in terms of cost and technology. The Film on Glass type mainly is used on consumer electronic products, such as self-service food ordering systems, PDAs, electronic dictionaries, mobile phones, stock and inventory management devices, POS accounting machines, credit card POS signature machines, medical monitor systems and the like. The Film on Glass type touch control panels also can be divided into digital type and analog type. The technology of the analog touch control panel further can be divided into 4-line, 5-line, 6-line and 8-line types. The technical principle of the touch control panel mainly bases on a screen touching by user's finger or other media to detect voltage, current, sound wave or infrared light according to different induction methods to identify the coordinates of the touching spot. For instance, the Film on Glass type uses the potential difference between a upper electrode and a lower electrode to detect the touch control point on the location of the pressing spot.
Whatever the type of the touch control panel, after the product is bonded with a glass baseboard and becomes a finished product, it has to go through a depressing electric field correction process through a touch control system. The purpose of the correction is to define a linear correction data table of an equal potential depressing curve of an applicable depressing electric field for the duty voltage of a selected installation site where operation the touch control system is to be performed. The definition is done by, first, preparing a linear correction database of a rated duty range voltage; after having determined the actual duty voltage of the touch control system on the operation site, comparing with the linear correction database to set the linear correction data table of the touch control system on the operation site.
However, after the touch control system has been installed on the actual operation site and connected to the actual duty voltage, the linear error of the touch control system could be undesirable. This phenomenon is more serious when the touch control panel is installed in an open space (especially in an outdoor environment). This is because the potential of the touch control system actually delivered by the transformed power supply on the operation site is not completely same as the duty voltage set at the shipment from the plant. A voltage variation is generated that affects the linearity accuracy. In addition, temperature, humidity and external interference also affect the potential and result in lower accuracy of the touch control system.